This invention relates generally to centrifugal compressors and, more particularly, to a method of making a pipe diffuser therefor.
Pipe diffusers, such as are shown and described in U.S. Pat. No. 3,333,762 issued to J. C. Vrana on Aug. 1, 1967, have long been used with centrifugal compressors in aircraft engines. Typically, an array of generally radially extending passages are circumferentially spaced and angled from the radial direction such that their center lines are all tangent to the same circle, referred to as the tangency circle. The geometry is such that, at the point where the passages mutually intersect, a semi-vaneless space is formed between the tangency circle and an outer circle called the leading edge circle. Since the intersection of adjacent coplanar cylinders is an ellipse, this semi-vaneless space is composed of an array of symmetrically located elliptical ridges at the intersections. When the diffuser structure is placed around a centrifugal impeller, the flow exiting from the impeller will enter at the tangency circle, flow through the semi-vaneless space, and then enter the plurality of discrete passages in the diffuser.
The aerodynamic merit of such a diffuser concept is that of obtaining an optimum aspect ratio and therefore relatively high efficiency. A feature of such a pipe diffuser structure is that the individual passages must extend radially inwardly to the extent that they intersect. The problem encountered during the drilling process is that as the drill commences to enter the adjacent passages, it tends to wander from the intended straight path along its axis. A typical method of dealing with this problem is to use metal plugs to fill the previously drilled holes so as to thereby present a uniform, solid medium, environment in the intersection area. After all the passages have been drilled, and the material disposed radially inside the tangency circle is removed, the metal plugs can be removed. However, such a process tends to be expensive in terms of time and material that are required.
It is therefore an object of the present invention to provide an improved method of making a pipe diffuser.
Another object of the present invention is the provision in a pipe diffuser for making the diffuser channels in an accurate and economical manner.
Yet another object of the present invention is the provision for a pipe diffuser which is economical to manufacture and effective in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.